1. Field of the Invention
The present invention relates to a sound field expansion system. The present invention particularly relates to a sound field expansion system which is applicable to a magnetic recording and reproducing apparatus, such as a video tape recorder (VTR), which plays back a magnetic tape on a common track on which a video signal and a time-axis-compressed Pulse Code Modulation (PCM) audio signal are recorded in a time share mode and on the same track of which an Audio Frequency Modulated (AFM) signal is recorded with the video signal in a frequency division multiplex mode. Still more particularly, the present invention relates to a sound field expansion system which can move or position various accoustic images over a wide sound field.
2. Description of the Prior Art
Conventional magnetic recording and reproducing apparatus, e.g., helical scan type video tape recorders (VTR), have recording tracks which slant across the magnetic tape and record video signals on the common tracks through the use of at least one rotary head. Since the audio signals are recorded by a stationary head, audio tracks lie along the elongated axis of the magnetic tape. In such magnetic recording and reproducing VTR apparatus, the rate of feed of the magnetic tape may be reduced to expand the recording time. But when the tape feed rate is reduced, the quality of the audio signals is also reduced. To improve the quality of the sound, a magnetic tape recording and reproducing apparatus has been developed which records the audio signals in the above-described video tracks by means of one or more rotary heads.
FIG. 1(A) shows an arrangement of a rotary drum and magnetic tape in the magnetic recording and reproducing apparatus (herinafter referred simply to as the "VTR") and FIG. 1(B) shows the recording format on the tracks, respectively.
In FIG. 1(A), the VTR includes a rotary drum 1, two rotary heads 2a and 2b, and a magnetic tape 3 wound around a portion of the periphery of the rotary drum 1 by means of guide pins 4 so that the tape 3 contacts the drum 1 over an angle of 180.degree.+.alpha., wherein .alpha.=30.degree.. This rotary contact area is sometimes referred to as a "wrap angle".
The audio signals to be recorded are alternatingly provided from associated recording circuitry to the rotary heads 2a, 2b. The audio signals are then recorded in the form of time-axis-compressed Pulse-Code-Modulated (PCM) audio signals SPA on tracks 5, 6, 7 obliquely formed on the tape 3 together with one-field video signals SV in respective predetermined regions of the tracks 5, 6, 7. Furthermore, a frequency-modulated audio (AFM) signal SA (constituted by a 1.5 MHz carrier wave) is recorded on the same track 5, 6, 7 with the video signal SV in a frequency share mode (i.e., frequency division multiplex mode). It is noted that numeral 8 denotes an auxiliary track located along a tape running direction and on which an audio signal (non-modulated) is usually recorded by means of a stationary head. The AFM audio signal is recorded with the audio signal frequency modulated and interposed between frequency bands of a low-band converted chrominance signal and luminance signal of the video signal. It is noted that in FIG. 1(B), an arrow mark a denotes a scanning direction of the rotary heads 2a, 2b and an arrow mark b denotes a running direction of the tape 3. In addition, the above-described PCM audio signal SPA is usually a stereo signal comprising an L (left) channel signal and R (right) channel signal but is rarely a monaural signal comprising an (R+L) signal and the AFMm audio signal is a monaural signal.
When the above-described signal SPA is recorded, the signal SPA recorded on each track 5, 6, 7 does not correspond to the above-described video signal SV recorded on the same track and the signal SPA is recorded with a delay of substantially one field interval of time. For example, the signal SPA recorded on the track 6 substantially corresponds to the signal SV which has been recorded on the previous track 5.
When the tape 3 is recorded in the above-described format, the signal SPA is further delayed by an interval of time substantially corresponding to one track. Hence, during the playback operation, the signal SPA is outputted with a delay substantially corresponding to two field intervals (about 33.3 msec.) and the above-described AFM signal is outputted from the tape 3 at the same time as the output of the above-described signal SV.
The above-described recording and reproducing method is exemplified by a Japanese Patent Application Unexamined Open No. Sho 58-94288 published on June 4, 1983 and has been put into practice in an 8 mm VTR.
If, in the conventional reproducing apparatus having two or more channels, a stereo audio source has been recorded, a sufficient effect of expanding a sound field can be achieved when such an audible sound field expansion processing during the playback operation is carried out. However, if a monaural audio source has been recorded, the effect of expanding the sound field cannot sufficiently be achieved and only an extremely weak reproduction of the sound field can be formed.
In addition, since the conventional sound field expansion system uses delay circuits constituted by BBDs (Bucket Brigade Device) or CCDs (Charge Coupled Device), and so forth, the circuit construction thereof is complex and the cost thereof is expensive. Hence, a relatively simple reproduced sound field results.
Especially, in a case when a music sound in which a human voice(s) is incorporated is reproduced, the reproduced sound is unnatural and difficult to hear since an echo effect on the human voice is unnecessarily emphasized.